1. Field of the Invention
The present invention relates to an aqueous fabric softener composition, i.e., a liquid softener composition, which can impart an excellent softness and elasticity (fluffiness) to various fibers, and is excellent in storage stability over a wide range of temperature. Further, the present invention relates to a quaternary ammonium salt which is useful as a base of the above-mentioned aqueous fabric softener composition and is nondetrimental to the natural environment because of its excellent biodegradability, and a process for the preparation thereof. Furthermore, the present invention relates to a use of the quaternary ammonium salt, and a method for imparting softness and elasticity to fibers which comprises using the quaternary ammonium salt.
2. Description of the Related Art
Fabric softeners for domestic use at the present time are generally in the form of a composition comprising di(hardened beef tallow alkyl)dimethylammonium chloride as the main component. The reason this quaternary ammonium salt is used as the main component in fabric softeners for domestic use is that the salt exerts an excellent softening effect on various fibers even when used in a small amount.
Although the above-mentioned quaternary ammonium salt exerts an excellent softening effect, it sometimes deteriorates the elasticity of fibers, in particular, cotton and thus imparts an oily hand to the fabrics when applied at a high concentration in order to further elevate the softening effect. Further, when stored for a long period of time, a fabric softener composition comprising the above-mentioned quaternary ammonium salt is easily thickened, gels or separates out in some cases due to its physicochemical properties.
Furthermore, there is a disadvantage that a quaternary ammonium salt having two long-chain alkyl groups, such as the above-mentioned di(hardened beef tallow alkyl)dimethylammonium chloride, has poor biodegradability.
Attempts have been made to eliminate or reduce these disadvantages of the conventional fabric softeners for domestic use and the conventional quaternary ammonium salts, which is a main component of the fabric softeners, by introducing an ester group or an amido group between a quaternary nitrogen atom and a long-chain alkyl group. For example, European Patent Publication-A No. 472,178 (published on Feb. 26, 1992) and U.S. Pat. No. 5,282,983 (assignee: Kao Corp.; date of patent: Feb. 1, 1994) corresponding hereto have disclosed a fabric softener composition comprising a di(long-chain alkyl) quaternary ammonium salt having ester and amido groups, which imparts an oily hand to the clothes treated therewith. Further, European Patent Publication-A No. 192,145 (published on Aug. 27, 1986) has disclosed a fabric softener composition comprising a di(long-chain alkyl) quaternary ammonium salt having ester and amido groups, which is highly dispersible in cold water without gelling.
Meanwhile, attempts have also been made to improve the storage stability of the fabric softener compositions comprising a quaternary ammonium salt with the use of an additive. Namely, in addition to the above-mentioned quaternary ammonium salt, various additives, such as polyoxyethylene-based nonionic surfactants, electrolytes and solvents, are employed in marketed softeners for domestic use so as to improve the storage stability to thereby keep them stable for a long period of time.
European Patent Publication-A No. 21,431 (published on Jan. 7, 1981) has disclosed a diester type quaternary ammonium salt as a base for fabric softeners that do not utilize di(long-chain alkyl) quaternary ammonium salts. However, the diester type quaternary ammonium salt is still unsatisfactory in both biodegradability and softening performance.
As described above, fabric softener compositions comprising a quaternary ammonium salt in the prior art are still unsatisfactory in softening performance, storage stability and biodegradability.
Accordingly, it is an object of the present invention to provide an aqueous fabric softener composition which shows a fully satisfactory performance in softening effect, elasticity (fluffiness) and storage stability, and to provide a quaternary ammonium salt which is suitable to incorporate into such an aqueous fabric softener composition, useful as a softener base and nondetrimental to the natural environment because of its excellent biodegradability, and a process for the preparation of this salt. Further, an object of the present invention is to provide a use of the quaternary ammonium salt, and to provide a method for imparting softness and elasticity to fibers which comprises using the quaternary ammonium salt.